In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long-term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower latency and so on (see non-patent literature 1). In addition, successor systems of LTE are also under study for the purpose of achieving further broadbandization and increased speed beyond LTE (referred to as, for example, “LTE-A (LTE-Advanced),” “FRA (Future Radio Access),” “4G,” “5G,” “5G+(plus),” “NR (New RAT),” “LTE Rel. 14,” “LTE Rel. 15 (or later versions),” and so on).
In existing LTE systems (for example, LTE Rel. 8 to 13), downlink (DL) and/or uplink (UL) communication are performed using one-ms subframes (also referred to as “transmission time intervals (TTIs)” and so on). These subframes are the time unit for transmitting one channel-encoded data packet, and serve as the unit of processing in, for example, scheduling, link adaptation, retransmission control (HARQ: Hybrid Automatic Repeat reQuest) and so on.
A radio base station controls the allocation (scheduling) of data for a user terminal, and reports the schedule of data to the user terminal using downlink control information (DCI). The user terminal controls receipt of DL data and transmission of uplink data based on the downlink control information. For example, in existing LTE systems, when a user terminal receives downlink control information that commands UL transmission (for example, a UL grant), after a predetermined period (for example, 4 ms later), the user terminal transmits uplink data in a predetermined subframe.